The search for processes to provide alternate feedstocks for chemicals, and particularly low to intermediate range olefins, has been prompted by the potential shortage of traditional petroleum reserves, and the increasing instability of international hydrocarbon resources.
One approach to the problem has been the utilization of the Fischer-Tropsch synthesis in producing a selective product distribution of olefinic hydrocarbons also containing paraffins, in varying olefin/paraffin ratios, depending on the catalyst composition, pretreatment procedures, and reaction conditions. Catalysts having various combinations of elements have been tested in the past, and the chief constituent element of the catalyst has been nickel, cobalt, iron or ruthenium.
Ruhrchemie Aktiengesellachaft disclosed in GB No. 1,512,743, GB No. 1,553,361 GB No. 1,553,362 and GB No. 1,553,363 catalysts pertaining to the selective production of C.sub.2 -C.sub.6 olefins from synthesis gas, comprising carbon monoxide and hydroqen. The inventions embody a process for the production of one or more unsaturated hydrocarbons comprising catalytic hydrogenation of carbon monoxide with hydrogen at 250.degree. C. to below 350.degree. C. and a total pressure of 10 to 30 bars in the presence of a catalyst which contains (a) one or more oxides selected from difficult-to-reduce oxides of metals from Group IVB of the Periodic Table or a lower oxide of Group V and/or Group VII; and (b) one or more metals selected from Group VIII of the Periodic table, the ratio by weight of the metal or metals of the one or more oxides (a) to the one or more oxides (b) being in the range 1:2 to 1:10. Additionally, the catalysts can contain a Group lA alkali metal, MgO and ZnO promoters. Good yields of unsaturated hydrocarbons, especially gaseous olefins were reported with these catalysts.
U.K. Patent No. 833,976 discloses a catalyst for the production of ethylene from carbon monoxide and hydrogen consisting of four components: the first a group including zinc oxides; the second group preferably being cobalt, although iron also can be used, with the proviso that the Group VIII metal component constitute not more than 10% of the total weight of the catalyst, and being activated by compounds which may include manganese oxide; a third group including an oxide of titanium and/or the rare earth elements; and the fourth group being a carbonate, oxide or hydroxide of an alkali metal. The reaction preferably is conducted at a temperature of 350.degree. C. to 520.degree. C., preferably 350.degree. C. to 450.degree. C.
U.S. Pat. No. 4,199,523 discloses a Fischer-Tropsch catalyst containing at least 60% iron. In addition, promoters such as copper and/or silver and alkali are described. Other additives, such as alkaline earth metal compounds, zinc oxide, manganese oxide, cerium oxide, vanadium oxide, chromium oxide and the like may be used.
U.S. Pat. No. 4,639,431 discloses a Fischer-Tropsch catalyst containing iron, a Group IIB metal such as zinc, with Group IA metal promoters with a lanthanide metal such as cerium which is sintered at temperatures ranging from 800-1200.degree. C.
Benbenek et al in Prezm Chem, Vol 65 (3) pp. 136-138 (1986) disclose a four component catalyst for converting synthesis gas to olefins; the catalyst comprising iron:copper:zinc oxide:potassium oxide in a weight ratio of 100:20:10:8.
However, what is desired in the art and which none of the above-identified art disclosures teach is a catalyst which exhibits high activity in the production of C.sub.2 -C.sub.20 alpha-olefins while concurrently maintaining high activity and selectivity under olefin producing conditions. Especially preferred is a catalyst which can generate high levels of alpha olefins in a hydrogen rich environment, where the H.sub.2 /CO molar ratio is 2/1 or higher, which is normally conducive to good activity maintenance but otherwise leads to a significant decrease in olefin/paraffin ratios.